#include #include #include #include #include #include #include #include #include using namespace std; int main(){ double px,py; cin >> px >> py; double qx,qy; cin >> qx >> qy; double dx=(px-qx); if(dx<0)dx*=-1; double dy=(py-qy); if(dy<0)dy*=-1; double dist=(dx+dy)/2; cout << dist << endl; return 0; }